#main{
    width: 1080px;
    margin: 0 auto;
}
#main img{
    width: 1080px;
}
#backTop{
    display: none;
    position: fixed;
    left: 50%;
    margin-left: 560px;
    bottom: 40px;
    width: 40px;
    height: 40px;
    background: url(../images/top_bg.png) no-repeat left top;
}